1. Field of Invention
This invention relates to the art of electric motors. This invention is specifically concerned with electric motors for driving piston pumps used in anti-locking brake devices for vehicles and the like.
2. Description of Related Art
Generally, examples of electric motors for driving piston pumps of this type include arrangements wherein the piston is caused to move reciprocally in the radial direction with respect to the armature shaft of the driving motor, e.g., arrangements used for anti-locking brakes. An example of such an arrangement is disclosed in Japanese Unexamined patent Publication No. 2-207184. In this arrangement, bearing of the armature shaft is accomplished by a pair of bearings provided at either side of an eccentric shaft linked to the piston side. The armature shaft is press fit to the inner ring of the pair of bearings. The armature shaft is press fit to the bearings when the shaft is aligned with each of the bearings. In the event that the outer rings of the bearings are press fit to the pump housing side, freedom in the radial direction is lost, and in the case that there is misalignment in both of the bearings, press fitting of the armature shaft cannot be performed for all practical purposes. Accordingly, the bearings are arranged so as to be loosely inserted into the pump housing to ensure freedom in the radial direction, however slight, thus handling misalignment.
However, with such an arrangement, not only does wobbling of the bearings in the radial direction due to receiving the load from the piston moving in the aforementioned radial direction cause noise and deterioration of pump performance, but other parts become necessary in order to prevent the bearings (which have been inserted loosely) from moving in the axial direction, requiring extra parts and complicated assembly. Because it is necessary to provide a space for setting a jig for assembling both bearings in a pump housing separately from a space for piston pump components, the resulting space for piston pump components becomes smaller, which creates a problem in that freedom in layout for the piston pump components in a pump housing is reduced.
In order to deal with such problems, an arrangement has been disclosed in Japanese Unexamined patent Publication No. 7-184344, wherein grooves are provided in the bearing outer ring and the member of the pump housing to which the bearing is to be inserted. Resin material is inserted into the aforementioned grooves so as to restrict movement in the axial and radial direction.
However, with such an arrangement, the endurance of the resin material is problematic, and not only is there the possibility that the bearings may return to the original state of being inserted loosely due to deterioration and the like of the resin over prolonged usage periods, but there is the problem that resin material in the grooves decreases work efficiency.